The invention relates to a brushless d.c. motor with a permanent magnet rotor with the recessing of a radial narrow air gap, a part of the flux emanating from the rotor being concentrated by a stationary magnetic flux conductor onto a stationary magnetic flux-sensitive control member which controls a commutator circuit. Both here and hereinafter a narrow air gap is understood to mean an air gap which is as narrow as it is used within practical manufacturing tolerances of electric motors.
As a function of changes in the magnetic flux flowing through it, the control member which can be, for example, an induction coil or a Hall generator, generates an electrical control signal which controls the commutator circuit as a function of the rotor position.
From U.S. Pat. No. 3,644,765, there is known a d.c. motor having a Hall generator for controlling the commutator circuit. This Hall generator is positioned between two magnetic flux conductors, the free end of one of which recesses an axial air gap and faces the permanent magnet of the rotor, while the other of which projects via its free end into an induction coil of the stator. This known motor requires an axial adjustment of the rotor relative to the stator during assembly in order to adjust the axial air gap of the magnetic flux conductor to the necessary predetermined value for the control signal of the commutator circuit. Furthermore, in this known motor the Hall generator takes up a considerable amount of space in an area betwen the rotor magnet and the induction coil which is critical from the standpoint of space requirements.
In a d.c. motor of the type shown in German DAS No. 1,911,836, a Hall generator for controlling the commutator circuit is positioned on that side of the stator induction coil which faces the rotor permanent magnet. It is therefore located in the stray flux range of the magnetic field emanating directly from the induction coil and indirectly from the rotor. The stray flux is concentrated onto the Hall generator by magnetic flux conductors directed toward the induction coil.